Conventional methods for the casting of metals by the overflow of molten metal include creating a flow of molten metal from a receptacle onto a cooling, moving, heat extracting substrate. In this manner, the metal is removed from the receptacle, solidified and spontaneously released from the surface of the substrate.
To obtain a uniform cast product having a given quality and dimensions, one must be able to pour or overflow the molten material at a controlled rate, i.e., to control the metal flow rate in a precise manner so as to keep it always constant in relation to the speed of removal of the solidified me&:al from the cooling, moving substrate.
Various methods have been utilized to control the uniformity of the molten material flow so that the solidified product has a desired uniformity. U.S. Pat. No. 3,522,836, issued Aug. 4, 1970 to King, and U.S. Pat. No. 3,605,863, issued Sept. 20, 1971 to King, teach a method and apparatus for manufacturing wire and the like by maintaining static equilibrium in molten material at the outlet of a nozzle to form a convex meniscus from which the material is continuously drawn off and solidified by means of a moving surface. The King patents utilize a piston which is driven downwardly into the molten material to force the molten material through a nozzle. The piston is driven in response to a signal from a relay switch which is activated by excitation of a relay. Two electrodes complete the electrical circuit in the King patents by the placement of one of the electrodes in the molten material and one electrode situated at the desired level above said molten material whereby when the level of the molten material reaches the second electrode the level is sufficient to flow out the nozzle. Furthermore, when the surface of the molten material rises to the desired level of the second electrode, electrical contact is made, closing the relay circuit, which stops a motor driving the piston. When, however, the surface of the molten metal is low, galvanic contact is interrupted, the relay is deenergized and the switch closes. The motor then turns on and the piston is driven downwardly, thereby raising the molten material level until the desired level of the second electrode is attained causing the motor to stop.
The method and apparatus of King, however, require an electrical conductivity through the molten material. The electrodes are subject to being partially dissolved in the melt or having melt solidify on them, either of which can change the effective location of the electrode and thereby change the melt level at which it activates the circuit. Furthermore, the King patents are not melt overflow procedures but are designed to drive molten material through a nozzle. Finally, the King patents do not rely on detection of changes in buoyant forces on the piston.
U.S. Pat. No. 4,592,410 shows a melt flow rate control system in which an entire tundish and its contents is weighed and the weight signal used to control a nozzle.
Other level control systems are shown in U.S. Pat. Nos. 3,478,808; 3,921,697; and 4,276,921.